Five years ago I was impressed with John Key. He showed real principle during the 2008 election campaign saying he would not lead a government that included Winston Peters. When pressed by an incredulous media, he calmly explained that if to be prime minister he needed NZ First he would step aside and let Helen Clark govern with him. His reason? He didn't trust Peters.

It was a master stroke and contributed more to National's victory over Clark than people realise. Peters was deeply unpopular. His twinkling charm had been replaced with a shifty sneer. Key's announcement followed Peters' denial he had received money from Owen Glenn, when in my opinion he clearly had.

Key revealed an integrity we rarely get from politicians. Voters were impressed. It made Clark awkwardly defensive and her reliance on Peters look unsavoury. It also destroyed Peters' traditional bargaining chip that he could work with either party and graphically signalled to centre-right voters that a vote for Peters was a vote for Clark - not him - to lead the country.

The gamble paid off. Peters and his party were dumped from Parliament. Clark lost her premiership and career.

Alas, since then a new man of dubious integrity has evolved. In 2011, his political tea party with John Banks went awry when his ridicule of others was accidentally recorded. Key's personal attacks and attempts to persuade the police to charge the hapless cameraman offender were loathsome.The man's reputation and livelihood were savaged by Key without a flicker of remorse.

When Kim Dotcom and SkyCity were revealed to have made "anonymous" donations to Banks' mayoral campaign, Key protected his ally saying he had complete confidence his minister hadn't known about the donations. At the same time he was saying he didn't want to read the police investigation on the scandal. Why? We know why.

Now Banks is appearing in the dock, Key has moved on, saying this week he'll go with Act no matter who they put up as leader and Epsom candidate. Sight unseen. Character has been replaced by expediency.

This brings us to Peter Dunne, a hypocrite who lectured other MPs on their ethics but became chief suspect as the source of secret papers leaked to a journalist. A few months ago Key said he couldn't trust Dunne but apparently now it's okay. This week, he welcomed Dunne back into his cabinet.

And to complete the circle, our Prime Minister has in effect offered Peters the Deputy Prime Minister's job in his next government. Has the NZ First leader changed from being untrustworthy or has our Prime Minister traded in his principles? It's a rhetorical question.